1. Field of the Invention
The present invention relates to a piezoelectric device for converting an input electric signal to an output electric signal through a piezoelectric vibrator.
2. Description of the Prior Art
Signal converters are applied, for example, to switching power supplies. Switching power supplies are used extensively as power supplies for telegraphic instruments, electric computers and so on. Conventional switching power supplies convert a power supply with direct current to an electric power with high frequency by using a high speed switching effect of a semiconductor, and then control and rectify the electric power to obtain a favorite direct current. In order to miniaturize switching power supplies, it is necessary to operate at higher switching frequencies and to size all sorts of parts down. However, an operation at higher switching frequencies brings damages on a semiconductor and an electromagnetic transformer, the damages increasing at 1 MHz and over. Therefore, it was difficult to more miniaturize switching power supplies. In order to minimize the damage on the semiconductor, it is necessary to improve a delay of a switching action generated in a switching circuit by means of the resonance and so on. In order to minimize the damage of the electromagnetic transformer, it is necessary to improve the materials of the electromagnetic transformer. However, remarkable improvements were difficult. Thus, various attempts to use a piezoelectric transformer in a switching power supply circuit were made. Conventional piezoelectric transformers include a polarization conversion type, a longitudinal vibration type and so on. The piezoelectric transformer of the polarization conversion type has a difficulty in a large amplitude action because of, for example, an acoustic damage of the materials, and an electric- or acoustic hysteresis phenomena of the materials. The piezoelectric transformer of the longitudinal vibration type has a difficulty in controlling the voltage ratio when a load resistance in a power supply circuit with the piezoelectric transformer is low. Moreover, the piezoelectric transformer of the longitudinal vibration type is easy to be broken by a large electric power. In addition, it is difficult to support a piezoelectric body, and it is necessary to reinforce the support in proportion to the increase of electric power, excessive reinforcement being easy to break the piezoelectric body.